In the fabrication of printed circuit boards (PCBs), the surface of metal foil traces or conductors of internal layers of the PCBs is often fairly rough. In general, the rougher the surface of metal foil traces associated with internal layers of a PCB, the stronger the bond between layers of the PCB.
The surface roughness of metal foil traces of a PCB, however, has an effect on the performance of the PCB. Typically, as the surface roughness of metal foil traces of a PCB increases, the electrical performance of the PCB decreases. For example, signal loss within a PCB generally increases as the roughness of metal foil traces increases. When signal loss becomes excessive, the performance of a PCB may be compromised.
Signal loss associated with a PCB may not be determined until after the PCB is fabricated, e.g., finished. Signal loss is generally measured during a signal-integrity analysis performed on an assembled PCB. However, the contribution of surface roughness of metal foil traces of internal layers of the PCB may not be determined using conventional roughness measurements, as conventional methods for measuring surface roughness may only be applied to raw foil, i.e., foil that has not yet been fabricated into an internal layer of a finished PCB. Thus, when it is determined that signal loss associated with a PCB is unacceptable, the contribution of surface roughness of metal foil traces of internal layers of the PCB may not be assessed.